This invention relates to methods of and apparatus for forming metal containers or the like, utilizing internal fluid pressure to expand a hollow metal preform or workpiece against a die cavity. In an important specific aspect, the invention is directed to methods of and apparatus for forming aluminum or other metal containers having a contoured shape, e.g. such as a bottle shape with asymmetrical features.
Metal cans are well known and widely used for beverages. Present day beverage can bodies, whether one-piece xe2x80x9cdrawn and ironedxe2x80x9d bodies, or bodies open at both ends (with a separate closure member at the bottom as well as at the top), generally have simple upright cylindrical side walls. It is sometimes desired, for reasons of aesthetics, consumer appeal and/or product identification, to impart a different and more complex shape to the side wall and/or bottom of a metal beverage container, and in particular, to provide a metal container with the shape of a bottle rather than an ordinary cylindrical can shape. Conventional can-producing operations, however, do not achieve such configurations.
For these and other purposes, it would be advantageous to provide convenient and effective methods of forming workpieces into bottle shapes or other complex shapes. Moreover, it would be useful to provide such procedures capable of forming contoured container shapes that are not radially symmetrical, to enhance the variety of designs obtainable.
The present invention in a first aspect broadly contemplates the provision of a method of forming a metal container of defined shape and lateral dimensions, comprising disposing a hollow metal preform having a closed end in a die cavity laterally enclosed by a die wall defining the shape and lateral dimensions, with a punch located at one end of the cavity and translatable into the cavity, the preform closed end being positioned in proximate facing relation to the punch and at least a portion of the preform being initially spaced inwardly from the die wall; subjecting the preform to internal fluid pressure to expand the preform outwardly into substantially full contact with the die wall, thereby to impart the defined shape and lateral dimensions to the preform, the fluid pressure exerting force, on the preform closed end, directed toward the aforesaid one end of the cavity; and, either before or after the preform begins to expand but before expansion of the preform is complete, translating the punch into the cavity to engage and displace the closed end of the preform in a direction opposite to the direction of force exerted by fluid pressure thereon, deforming the closed end of the preform. Translation of the punch is effected by a ram which is capable of applying sufficient force to the punch to displace and deform the preform. This method will sometimes be referred to herein as a pressure-ram-forming (PRF) procedure, because the container is formed both by applied internal fluid pressure and by the translation of the punch by the ram.
As a further feature of the invention, the punch has a contoured surface, and the closed end of the preform is deformed so as to conform to the contoured surface. For instance, the punch may have a domed contour, the closed end of the preform being deformed into the domed contour.
The defined shape, in which the container is formed, may be a bottle shape including a neck portion and a body portion larger in lateral dimensions than the neck portion, the die cavity having a long axis, the preform having a long axis and being disposed substantially coaxially within the cavity, and the punch being translatable along the long axis of the cavity.
Advantageously and preferably, the die wall comprises a split die separable for removal of the formed container. The term xe2x80x9csplit diexe2x80x9d as used herein refers to a die made up of two or more mating segments around the periphery of the die cavity. With a split die, the defined shape may be asymmetric about the long axis of the cavity.
The punch is preferably initially positioned close to or in contact with the preform closed end, before the application of fluid pressure, in order to limit axial lengthening of the preform by the fluid pressure. Translation of the punch may be initiated after the expanding lower portion of the preform has come into contact with the die wall.
The preform, for forming a bottle-shaped container or the like, is preferably an elongated and initially generally cylindrical workpiece having an open end opposite its closed end. In particular embodiments of the invention, it may be substantially equal in diameter to the neck portion of the bottle shape, and may have sufficient formability to be expandable to the defined shape in a single pressure forming operation. If it lacks such formability, preliminary steps of placing the workpiece in a die cavity smaller than the first-mentioned die cavity, and subjecting the workpiece therein to internal fluid pressure to expand the workpiece to an intermediate size and shape smaller than the defined shape and lateral dimensions, are performed prior to the PRF method described above.
Alternatively, if the elongated and initially generally cylindrical workpiece is larger in initial diameter than the neck portion of the bottle shape, the method of forming a bottle-shaped container may include a further step of subjecting the workpiece, adjacent its open end, to a necking operation to form a neck portion of reduced diameter, after performance of the PRF procedure.
Alternatively, the diameter of the neck area of the preform is reduced using a die necking procedure. This die necking procedure could be applied before the expansion stage.
The preform may be an aluminum preform (the term xe2x80x9caluminumxe2x80x9d herein being used to refer to aluminum-based alloys as well as pure aluminum metal) and may be made from aluminum sheet having a recrystallized or recovered microstructure with a gauge in a range of about 0.25 to about 1.5 mm. It may be produced as a closed end cylinder by subjecting the sheet to a draw-redraw operation or back extrusion.
During the step of subjecting the preform to internal fluid pressure, the fluid pressure within the preform occurs in successive stages of (i) rising to a first peak before expansion of the preform begins, (ii) dropping to a minimum value as expansion commences, (iii) rising gradually to an intermediate value as expansion proceeds until the preform is in extended though not complete contact with the die wall, and (iv) rising from the intermediate pressure during completion of preform expansion. Stated with reference to this sequence of pressure stages, the initiation of translation of the punch to displace and deform the closed end of the preform in a preferred embodiment of the invention occurs substantially at the end of stage (iii).
Typically, when the internal fluid pressure is applied, the closed end of the preform assumes an enlarged and generally hemispherical configuration as the preform comes into contact with the die wall; and initiation of translation of the punch occurs substantially at the time that the preform closed end assumes this configuration.
Also in accordance with the invention, the step of subjecting the preform to internal fluid pressure comprises simultaneously applying internal positive fluid pressure and external positive fluid pressure to the preform in the cavity, the internal positive fluid pressure being higher than the external positive fluid pressure. The internal and external pressure are respectively provided by two independently controllable pressure systems. Strain rate in the preform is controlled by independently controlling the internal and external positive fluid pressures to which the preform is simultaneously subjected for varying the differential between the internal positive fluid pressure and the external positive fluid pressure. In this way, more precise control of the strain rates may be achieved. In addition, the increased hydrostatic pressure may reduce deleterious effects of damage (voids) associated with the microstructure of the material.
According to a still further feature of the invention, it has been found to be advantageous to apply heat during expansion of the preform, such as to induce a temperature gradient in the preform. By adding heaters to the punch, a temperature gradient is induced in the preform from the bottom up. Separate heaters may be added at the top of the die which induce a temperature gradient in the preform from the top down. Further heaters may be included in the side walls of the die cavity.
It has also been found to be advantageous to have the punch in contact with the bottom of the preform before the start of the expansion phase and to apply some axial load by the punch throughout the expansion phase. With this procedure where the punch applies some axial load to the closed end of the preform throughout the expansion phase, the displacement and deformation of the preform closed end are preferably not carried out until completion of the expansion phase.
Also in accordance with the invention, the aforementioned split die may comprise a plurality of split inserts disposed in tandem along the axis of the die cavity for defining successive portions of the defined container shape and separable for removal of the formed container. Conveniently the split inserts are removably and replaceably received within a split holder that maintains the inserts in fixed die-cavity-defining position during expansion of the preform. At least one of the inserts may have an inner surface bearing a relief feature for imparting a corresponding relief feature to the container; the method of the invention may include the additional step of selecting one or more inserts from a group of interchangeable inserts having inner surfaces respectively bearing different relief features, and disposing the selected insert or inserts in the split holder for forming a container.
Internal and external positive fluid pressures may be applied by feeding gas to the interior of the preform and to the die cavity externally of the preform, respectively, through separate channels. Heat may be applied to the preform by multiple groups of heating elements respectively incorporated in upper and lower portions of the die structure and under independent temperature control for controlling temperature gradient in the preform. Additionally or alternatively, heat may be applied to the preform by a heating element disposed within the preform substantially coaxially therewith; and heat may be further supplied to the preform by heating the punch.
In addition, where the neck portion of the desired defined container shape includes a screw thread or lug for securing a screw closure to the formed container, and/or a neck ring, the die wall may have a neck portion with a thread or lug formed therein for imparting a thread to the preform during expansion of the preform.
The invention in a further aspect contemplates the provision of apparatus for forming a metal container of defined shape and lateral dimensions from a hollow metal preform having a closed end, comprising die structure providing a die cavity for receiving the preform therein with at least a portion of the preform being initially spaced inwardly from the die wall and the preform closed end facing one end of the cavity, the cavity having a die wall defining the aforesaid shape and lateral dimensions; a punch located at one end of the cavity and translatable into the cavity such that the closed end of a preform received within the cavity is positioned in proximate facing relation to the punch; and a fluid pressure supply for subjecting a preform within the cavity to internal fluid pressure to expand the preform outwardly into substantially full contact with the die wall, thereby to impart the aforesaid defined shape and lateral dimensions to the preform, the fluid pressure exerting force, on the closed end of the preform, directed toward the aforesaid one end of the cavity, the die cavity having a second end opposed to the aforesaid one end and an axis extending therebetween; wherein the die wall comprises a split die including a plurality of split inserts disposed in tandem along the axis for defining successive portions of the aforesaid defined shape and separable for removal of the formed container from the cavity. This apparatus may also include one or more of the additional features of the inserts, insert holders, heating and pressure arrangements, and neck thread or lug forming arrangements, described above with reference to the method of the invention.
Further features and advantages of the invention will be apparent from the detailed description hereinafter set forth, together with the accompanying drawings.